This invention relates to uncrosslinked liquid oligomers containing polymerizable groups that can be crosslinked using ultraviolet (UV) light without adding costly photoinitiators. The uncrosslinked liquid Michael Addition oligomers are prepared in the presence of catalysts having both an epoxy moiety and a quaternary salt. The uncrosslinked liquid Michael Addition oligomers prepared using the desired catalyst have lower viscosities and lower resin colors, and on crosslinking, lower film color than the same uncrosslinked liquid Michael Addition oligomers prepared in the presence of catalysts commonly used for such purposes.
The Michael Addition of beta-dicarbonyl donor compounds to multiacrylate acceptor compounds to make crosslinked polymers has been described in the literature. For example, Mozner and Rheinberger reported the Michael addition of acetoacetates to triacrylates and tetraacrylates (Macromolecular Rapid Communications 16, 135-138, 1995). The products formed were crosslinked (cured) gels. In one of the reactions, Mozner added one mole of trimethylol propane triacrylate (TMPTA) having 3 functional groups to one mole of polyethylene glycol (600 molecular weight) diacetoacetate (PEG-600-DM), having two functional groups. (Each xe2x80x9cacetoacetate functional groupxe2x80x9d reacts twice; thus each mole of diacetoacetate has four reactive equivalents.) 
Mole Ratio of TMPTA:PEG 600 DAA=1:1
Ratio of acrylate:acetoacetate functional groups=3:2
Ratio of reactive equivalents=3:4
U.S. Pat. Nos. 5,945,489 and 6,025,410 issued to Ashland Inc. disclose uncrosslinked liquid oligomeric compositions made by the Michael Addition reaction of acetoacetate functional donor compounds with multifunctional acrylate acceptor compounds in the presence of strong base catalysts such as diazabicycloundecene, diazabicyclononane and gaunidines. The contents of U.S. Pat. Nos. 5,945,489 and 6,025,410 are incorporated herein by reference. U.S. Pat. No. 5,565,525 discloses resin compositions curable through the Michael Addition reaction. The crosslinking reaction is catalyzed with a quaternary ammonium compound or other onium salt in the presence of an epoxide. The product of the Michael Addition reaction according to U.S. Pat. No. 5,565,525 is a cured, crosslinked composition and similar to compositions described in xe2x80x9cMacromolecular Rapid Communicationsxe2x80x9d in that they form solids.
In contrast according to the invention it has been found that liquid, oligomeric acrylic compositions can be prepared via the Michael Addition reaction in the presence of a catalyst system comprising an epoxide moiety and a quaternary salt.
This invention is the discovery that certain liquid uncrosslinked acrylic oligomers prepared via the Michael Addition reaction, using Michael donors such as beta keto esters and Michael acceptors such as acrylates, in specified ratios and in the presence of a catalyst system having an epoxy moiety and a quaternary salt, results in uncrosslinked liquid Michael Addition acrylic oligomers having lower viscosity and lower color compared to Michael Addition oligomers prepared in the presence of strong base catalysts. The oligomers of the present invention are photopolymerizable in the absence of photoinitiators. Polymerized (cured) films are lower in color than those produced from resins made with strong bases and color stability upon exposure to elevated temperatures and/or UV radiation (i.e., sunlight) is greatly enhanced.